The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, the thermal efficiency of heat engines increases when the compression ratio is high, and in spark ignition engines, the thermal efficiency increases when the ignition timing is advanced up to a predetermined level.
However, when the ignition timing is advanced with a high compression ratio in the spark ignition engines, abnormal combustion is generated and the engines may be damaged, so that there is a limit in advance of the ignition timing and accordingly the output is necessarily reduced.
A VCR (Variable Compression Ratio) apparatus is an apparatus that changes the compression ratio of a gas mixture in accordance with the operation state of an engine.
According to a variable compression ratio engine that varies the compression ratio, it improves the fuel efficiency by increasing the compression ratio of a gas mixture under a low load condition and prevents knocking and improves the output by reducing the compression ratio of the gas mixture under a high load condition.
In a case of the current diesel engine, to meet the enhanced exhaust gas regulations, the low temperature combustion is realized by reducing the compression ratio through the large volume of the piston combustion chamber, since the cold start performance is deteriorated depending on the compression ratio reduction, a glow system is manufactured of a ceramic material to enhance a rigidity thereof and a separate control unit controlling the glow system is added such that a manufacturing cost is increased.
Accordingly, research for a new structure realizing the variable compression ratio by controlling the position of the piston through a relatively simple structure has been undertaken, and a structure raising or lowering the piston by rotating an eccentric cam through a hydraulic pressure has been developed, however the hydraulic line for forward rotating or backward rotating the eccentric cam is respectively formed such that the structure thereof is complicated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.